"The mechanism thought to be responsible for reduced risk of incident HIV-1 infection in circumcised males is the presence of a significantly higher concentration of Langerhans cells, which are target cells for HIV-1 in the mucosal layer of the foreskin(19). Additionally, keratin is believed to provide a protective barrier against HIV-1 infection(20). The penile shaft and outer foreskin surface are well keratinized, while the inner mucosal layer of the foreskin is not(21). It is also argued that the sensitive foreskin may be more susceptible to micro-abrasion during sexual intercourse, which could provides an entry for STIs and HIV(22)."
The surprising and perplexing significant inverse association between reported female circumcision and HIV serpositivity (my emphasis -- PZ) has not been explained by other variables available and examined in these analyses
As no biological mechanism seems plausible, we conclude that it is due to irreducible confounding
"Cutaneous thickness and degree of keratinization (my emphasis -- PZ) are relatively high on the mons pubis and labia majora, but decrease over the anterior portions of the clitoris, and decline progressively from the outer surface to the inner surface of the labia minora."
"Three specialised cells -- melanocytes, Langerhans cells, and Merkel cells -- also reside in the epidermis."
As in the case of the foreskin, we see here that keratin is more a feature of the outer surface of the labia minora than of their inner surface. Moreover, we see that Langerhans cells are present in the vulva, as well as on the foreskin. There are various types of female circumcision, but already we see here what the biological mechanism might be for reduced HIV risk in circumcised females.
It is typical of the academic lies that dominate our Feminised world, that: